It is known practice to dye keratin fibers, and in particular human hair, with dye compositions containing oxidation dye precursors, such as ortho- or para-phenylenediamines, ortho- or para-aminophenols, and heterocyclic compounds, which are generally referred to as oxidation bases. These oxidation bases are colorless or weakly colored compounds which, when combined with oxidizing products, may give rise to colored compounds by a process of oxidative condensation.
It is also known that the shades obtained with these oxidation bases may be varied by combining them with couplers or coloration modifiers, the latter being chosen, for example, from aromatic meta-diaminobenzenes, meta-aminophenols, meta-diphenols and certain heterocyclic compounds such as indole compounds.
The variety of molecules used as oxidation bases and couplers makes it possible to obtain a wide range of colors.
The “permanent” coloration obtained by means of these oxidation dyes should, moreover, satisfy a number of requirements. The dyes should have no toxicological drawbacks, should allow shades of the desired intensity to be obtained, and/or should have good resistance to external agents such as light, bad weather, washing, permanent waving, perspiration and rubbing.
The dyes should also allow white hairs to be covered and, ideally, be as unselective as possible, i.e., allow the smallest possible differences in coloration to be produced over the entire length of the same keratin fiber, which is generally differently sensitized (i.e., damaged) between its end and its root.